PRELIMINARY
CY14B104L, CY14B104N
Document #: 001-07102 Rev. *F
Page 4 of 22
Device Operation
The CY14B104L/CY14B104N nvSRAM is made up of two
functional components paired in the same physical cell. They are
an SRAM memory cell and a nonvolatile QuantumTrap cell. The
SRAM memory cell operates as a standard fast static RAM. Data
in the SRAM is transferred to the nonvolatile cell (the STORE
operation), or from the nonvolatile cell to the SRAM (the RECALL
operation). Using this unique architecture all cells are stored and
recalled in parallel. During the STORE and RECALL operations
SRAM
read
and
write
operations
are
inhibited.
The
CY14B104L/CY14B104N supports infinite reads and writes
similar to a typical SRAM. In addition, it provides infinite RECALL
operations from the nonvolatile cells and up to 200K STORE
operations.
SRAM Read
The CY14B104L/CY14B104N performs a READ cycle when CE
and OE are LOW, and WE and HSB are HIGH. The address
specified on pins A0-18 or A0-17 determines which of the 524,288
data bytes or 262,144 words of 16 bits each is accessed. When
the read is initiated by an address transition, the outputs are valid
after a delay of tAA (read cycle #1). If the read is initiated by CE
or OE, the outputs are valid at tACE or at tDOE, whichever is later
(read cycle #2). The data outputs repeatedly respond to address
changes within the tAA access time without the need for transi-
tions on any control input pins. This remains valid until another
address change or until CE or OE is brought HIGH, or WE or
HSB is brought LOW.
SRAM Write
A WRITE cycle is performed whenever CE and WE are LOW and
HSB is HIGH. The address inputs must be stable before entering
the WRITE cycle and must remain stable until either CE or WE
goes high at the end of the cycle. The data on the common IO
pins DQ0–15 are written into the memory if the data is valid tSD
before the end of a WE controlled WRITE or before the end of
an CE controlled WRITE. It is recommended that OE be kept
HIGH during the entire WRITE cycle to avoid data bus contention
on common IO lines. If OE is left LOW, internal circuitry turns off
the output buffers tHZWE after WE goes LOW.
AutoStore Operation
The CY14B104L/CY14B104N stores data to the nvSRAM using
one of the following three storage operations: Hardware Store
activated by HSB; Software Store activated by an address
sequence; AutoStore on device power down. The AutoStore
operation is a unique feature of QuantumTrap technology and is
enabled by default on the CY14B104L/CY14B104N.
During a normal operation, the device draws current from VCC to
charge a capacitor connected to the VCAP pin. This stored
charge is used by the chip to perform a single STORE operation.
If the voltage on the VCC pin drops below VSWITCH, the part
automatically disconnects the VCAP pin from VCC. A STORE
operation is initiated with power provided by the VCAP capacitor.
Figure 4 shows the proper connection of the storage capacitor
(VCAP) for automatic store operation. Refer to the section DC
Electrical Characteristics on page 7 for the size of VCAP.
To reduce unnecessary nonvolatile stores, AutoStore and
Hardware Store operations are ignored unless at least one
WRITE operation has taken place since the most recent STORE
or RECALL cycle. Software initiated STORE cycles are
performed regardless of whether a WRITE operation has taken
place. Monitor the HSB signal by the system to detect if an
AutoStore cycle is in progress.
Figure 4. AutoStore Mode
Hardware STORE Operation
The CY14B104L/CY14B104N provides the HSB pin for
controlling and acknowledging the STORE operations. Use the
HSB pin to request a hardware STORE cycle. When the HSB pin
is driven LOW, the CY14B104L/CY14B104N conditionally
initiates a STORE operation after tDELAY. An actual STORE cycle
only begins if a WRITE to the SRAM took place since the last
STORE or RECALL cycle. The HSB pin also acts as an open
drain driver that is internally driven LOW to indicate a busy
condition while the STORE (initiated by any means) is in
progress.
SRAM READ and WRITE operations that are in progress when
HSB is driven LOW by any means are given time to complete
before the STORE operation is initiated. After HSB goes LOW,
the CY14B104L/CY14B104N continues SRAM operations for
tDELAY. During tDELAY, multiple SRAM READ operations may take
place. If a WRITE is in progress when HSB is pulled low it is
allowed a time, tDELAY to complete. However, any SRAM WRITE
cycles requested after HSB goes LOW is inhibited until HSB
returns HIGH.
During any STORE operation, regardless of how it was initiated,
the CY14B104L/CY14B104N continues to drive the HSB pin
LOW, releasing it only when the STORE is complete. Upon
completion
of
the
STORE
operation,
the
CY14B104L/CY14B104N remains disabled until the HSB pin
returns HIGH. Leave the HSB unconnected if it is not used.
VCC
VCC
VCAP
WE
VCC
VCC
VCAP
-
+
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